The present invention relates to the removal of waterborne metal contaminants from water. In particular, the invention relates to a filter media which removes metal contaminants from water passed through the filter media.
An area of increasing concern in the environmental sciences and engineering is the treatment of metals such as Cd, Cu, Zn, Ni, Pb, and Cr, which become waterborne and are carried by rain water run-off and the like to environmentally sensitive areas. As used herein, metals being xe2x80x9cwaterbornexe2x80x9d means being transported by water in any manner, whether the metal is actually in solution, suspended in water through a particulate bond or a colloidal bond, or simply physically carried by the velocity of flowing water. One of the most common manners in which metals become waterborne is through entrainment with storm water run off from road surfaces. The above metals are typically deposited on the road surface though vehicle exhaust, fluid leakage, vehicular wear, pavement degradation and pavement maintenance. Subsequent rainfall entrains the metals and transports the metals to the area in which storm water run-off accumulates. Typically, 60% to 80% of these metals are dissolved in the run-off water, while the remaining percentage is suspended by other mechanisms such as those mentioned above.
It is desirable to intercept the runoff and remove the metals prior to allowing the water to continue to its natural drainage areas. One method of removing the waterborne metals is to pass the water through a sorbent filter media. One of the most common media for removing particulate bound metals from water is sand. However sand has very little capacity for removal of dissolved metals and therefore, is generally not considered effective in removing dissolved metals. Granular activated carbon (GAC) has long used as a media for removing dissolved metals. However, GAC has relatively little absorptive capacity and thus, absorbed metals must frequently be removed or the GAC xe2x80x9crecharged.xe2x80x9d Also, GAC has very little compressive strength. Any application which places a load on the GAC material may cause crushing and a greatly reduce absorptive capacity of the GAC.
A much more recently developed sorbent media is iron oxide coated sand (IOCS). IOCS is formed by coating silica sand with a thin layer of iron oxide and it has been shown to be an effective sorbent media for metals. Iron oxides and hydroxides possess little or no permanent surface charge, but will take on a positive or negative surface charge in the presence of protons or hydroxyl ions. In other words, depending on the pH of the solution in which the iron oxide is place, the iron oxide may take on a net positive or negative charge. A substance which exhibits a net positive or negative charge depending on the pH level may be referred to as an xe2x80x9camphotericxe2x80x9d substance.
Iron oxide typically has a neutral charge in a pH range of approximately 7 to 8. When the pH rises above approximately 8, the iron oxide becomes more negatively charged. Thus, positively charged metal ions borne by water passing over the negatively charged iron oxide will tend to bond to the iron oxide and be sorbed from the water. Conversely, if the pH falls below approximately 7, the iron oxide becomes positively charged and is less likely to bond with metal ions. The pH at which the net surface charge of a particle is zero is denominated the point of zero charge or xe2x80x9cpzcxe2x80x9d.
One major disadvantage of IOCS is that the oxide coating is not sufficiently durable. The comparatively smooth surface of sand particles tends to result in the oxide coating flaking off. Attempts to avoid this flaking have led to time consuming sand preparation efforts such as cleaning the sand of organics and applying a scratch surface to the sand before applying the oxide coating. However, even with these preparation efforts, IOCS still exhibits considerable flaking and thus a lack of oxide coating durability.
The smooth surface of sand is also disadvantageous from the standpoint of providing a comparatively low specific surface area (SSA). The specific surface area of a material is generally defined as the surface area per unit mass with the typical unit being m2/gm. As used herein, specific surface area means the total area on the surface of the material in addition to any available porous internal surface area (such as found the GAC discussed above). The greater the surface area of the substrate, the greater the surface area of oxide coating which will be exposed to waterborne metals. Thus, it is desirable to provide a substrate with as great of an SSA as possible considering other design restraints. The SSA of sand is typically about 0.05 to about 0.10 m2/gm.
Another problem found in IOCS is the tendency of the oxide coating to crystallize. When the coating crystallizes, the crystals set up a uniform lattice which does not maximize the surface area of the coating. The surface area of the coating is much more optimal if the oxide molecules are randomly distributed in a non-lattice or xe2x80x9camorphousxe2x80x9d fashion. For example, the SSA of IOCS may reach 85 m2/gm if a method of sufficiently inhibiting crystallization could be provided. However, a purely crystallized oxide coating may have a SSA as low as 5 m2/gm. What is needed in the art is a manner to reliably inhibit crystallization in IOCS. Even more desirable would be a substrate other than sand which has a higher SSA than sand and a superior tendency to inhibit crystallization. It would also be desirable to provide substrates which could simultaneously act as a filter and provide other functions, such as providing a roadway pavement or parking pavement. Another desirable characteristic of a substrate (such as porous concrete) would be providing pH elevation to the fluid stream being treated.
One embodiment of the present invention is an adsorptive-filtration media for the capture of waterborne or airborne constituents. The media comprising a granular substrate and an amphoteric compound bonded to the substrate in the presence of a crystal inhibiting agent.
Another embodiment of the present invention includes an adsorptive-filtration media which comprises a substrate having a specific gravity of less than 1.0 and an amphoteric compound bonded to the substrate.
Another embodiment is a pavement material for the capture of waterborne constituents. The pavement material comprises a porous pavement substrate and an amphoteric compound bonded to the substrate.
Another embodiment includes a process for producing an adsorptive-filtration media for the capture of waterborne or airborne constituents. The process comprises the steps of providing a substrate with a specific surface area of greater than 0.1 m2/gm, introducing the substrate to an amphoteric metal solution, and drying the substrate.
Another embodiment includes an adsorptive-filtration media which comprises a substrate with a specific surface area of greater than 0.1 m2/gm and an amphoteric compound bonded to the substrate.
A further embodiment includes a storm water storage basin capable of supporting vehicular traffic. The basin comprise a layer of porous pavement having a hydraulic conductivity of more than 0.0001 cm/sec. The layer of porous pavement is at least 3 inches in depth, and the layer has a length and a width wherein the ratio between the length and the width is less than 20.
Another embodiment includes a method for producing a porous, cementitious material. The method includes the steps of providing and thoroughly mixing cement and aggregate, mixing water with the cement and aggregate into a slurry while maintaining a water to cement ratio of less than one, initiating curing of said slurry under pressure and in the presence of steam, and continuing the curing at ambient temperature and pressure until the cementitious material is substantially dry.
Another embodiment is a roadway with a gravel shoulder for the removal of waterborne ionic constituents. The roadway comprises a pavement section and a gravel shoulder section adjacent the pavement section. The gravel shoulder has a depth of at least 3 inches and includes gravel coated with an amphoteric compound.
Another embodiment includes a method of constructing a sub-base for the removal of waterborne constituents. The method includes the steps of placing a layer of uncompacted sub-base material; distributing upon the layer a solution containing an amphoteric compound; and compacting the layer to a selected density.
Another embodiment is an adsorptive-filtration media for the capture of waterborne or airborne constituents. The media comprises a flexible, planar, porous substrate; and an amphoteric compound bonded to said substrate.
Another embodiment is a drainage pipe capable of capturing waterborne constituents. The drainage pipe comprise a length of pipe having an interior surface, at least a portion of the surface being designed to be in contact with water. An amphoteric compound is then applied to the portion of the surface designed to be in contact with water.
Another embodiment of the invention includes a process for creating a filtering media for the capture of waterborne or airborne constituents. The process comprises the steps of providing a filter substrate; applying a first coating of an iron oxide compound to the substrate; and applying a second coating of a manganese oxide compound to the substrate.
Another embodiment of the invention includes a roadway with a shoulder forming a filter for constituents. The roadway comprises a roadway pavement section and a cementitious, porous, shoulder adjacent the pavement section and the shoulder having an amphoteric compound applied thereto.
Another embodiment provides an absorptive-filtration media have a porous structure of a fixed matrix and a porosity of approximately 0.05 to 0.6 and an amphoteric.
Another embodiment provides an adsorptive-filtration media having a granular substrate and an amphoteric compound formed of a manganese oxide formed on the substrate.
A another embodiment includes a method for forming a porous pavement roadway. This method includes the steps of providing and thoroughly mixing cement and aggregate; mixing water with the cement and aggregate forming it into a slurry while maintaining a water to cement ratio of less than one; and placing the slurry into a roadway bed.